In the past, various different types of control devices, such as fluid pressure actuated switches for instance, were utilized in an automotive type air conditioning system to control the energization and deenergization of a clutch operated compressor in such system in response to a preselected low and a preselected high fluid pressure measured at a preselected point in such system, such as in an accumulator of such system for instance.
In some of the past control devices, a fluid pressure responsive member, such as a diaphragm or the like for instance, was sealably interposed in a control device housing so as to define therein a fluid pressure chamber and a switch means accommodating chamber adjacent opposite sides of the diaphragm, respectively. A snap disc, which may have various different configurations so as to be movable between a stable configuration and an unstable configuration, was provided with a circumferential edge seated in the switch means accommodating chamber on the control device housing and adjacent the diaphragm, and switch means operable generally between make and break positions for controlling an electrical circuit through the control device was disposed in the switch means accommodating chamber generally adjacent the snap disc. Thus, the diaphragm was movable in response to a preselected fluid pressure acting thereon in the fluid pressure chamber to effect the application of a motive or applied force to the snap disc thereby to cause snap-action movement of the snap disc from the stable configuration thereof toward the generally inverted or unstable configuration thereof. When the snap disc was so moved to its unstable configuration, it effected the movement of the switch means from its break position to its make position. Thereafter, in response to a preselected reduction in the fluid pressure in the fluid pressure chamber which effected a corresponding reduction in the motive force applied by the diaphragm of the snap disc, the snap disc returned with snap-action from its unstable configuration to its stable configuration thereby to permit the return movement of the switch means from its make position to its break position. Of course, in its make and break positions, the switch means completed and interrupted and circuit through the control device which effected the energization and deenergization of the aforementioned clutch device controlled or actuated compressor, respectively.
One of the disadvantageous or undesirable features of at least some of the past control devices is believed to be that the transition of the snap disc between the stable and unstable configurations thereof resulted in objectionable noise, such as a clicking noise for instance, which was audible in the passenger compartment of the automobile. For instance, since these control devices were mounted to the air conditioner accumulator, it is believed that the aforementioned objectionable noise was transmitted directly into the passenger compartment of the automobile. Another disadvantageous or undesirable feature of the past control devices is believed to be that the pumping action of the diaphragm resulting from the snap-action of the snap disc effected an undesirably large movement of ambient atmospheric air into and out of the switch means accommodating chamber of such control device; therefore, under certain atmospheric conditions, such pumping of the ambient air is believed to have resulted in the formation of condensation and/or the formation of frost within the switch means accommodating chamber of such control device which is also believed to be a disadvantageous or undesirable feature.